1. Field of Invention
The present invention relates to a heat pump system for a vehicle and a control method thereof. More particularly, the present invention relates to a heat pump system for a vehicle in which a water cooled condenser is applied to an electric vehicle and waste heat of a motor and an electronic device is used to improve heating performance and dehumidifying performance, and a control method thereof
2. Description of Related Art
Generally, an air conditioning system for a vehicle includes an air conditioning module for warming or cooling a cabin of the vehicle.
Such an air conditioning module circulates a heat-exchanging medium through a condenser, a receiver drier, an expansion valve, and an evaporator by operation of a compressor. The heat-exchanging medium then flows back to the compressor. In this process, the air conditioning module warms the cabin of the vehicle through heat exchange at the evaporator or cools the cabin of the vehicle through heat exchange with a coolant at a heater.
Meanwhile, energy efficiency and environmental pollution are of increasing concern, and environmentally-friendly vehicles substituting for vehicles having an internal combustion engine have been researched. Such environmentally-friendly vehicles include electric vehicles using a fuel cell or electricity as a power source, or hybrid vehicles driven by an engine and an electric battery.
An air conditioning system of an electric vehicle among the environmentally-friendly vehicles, different from that of a typical vehicle, does not use a separate heater. An air conditioning system applied to an electric vehicle is typically called a heat pump system.
According to the heat pump system, a high temperature/pressure gaseous refrigerant compressed at a compressor is condensed at a condenser and then is supplied to an evaporator passing through a receiver drier and an expansion valve in a cooling mode in the summer. The gaseous refrigerant is evaporated at the evaporator and lowers the temperature and humidity of the cabin. However, the heat pump system has characteristics that the high temperature/pressure gaseous refrigerant is used as a heater medium in a warming mode in the winter.
That is, the high temperature/pressure gaseous refrigerant is supplied not to an exterior condenser but to an interior condenser through a valve, and is heat-exchanged with air in the warming mode in the electric vehicle. The heat-exchanged air passes through a positive temperature coefficient (PTC) heater. After that, the air flows into the cabin of the vehicle and raises the cabin temperature of the vehicle.
The high temperature/pressure gaseous refrigerant flowing into the interior condenser is condensed through heat exchange with the air and flows out in a state of liquid refrigerant.
However, a conventional heat pump system as described above is an air-cooled type in which the refrigerant is cooled by outside air, and therefore there is a problem that the structure of the heat exchanger and constituent elements are complicated.
Also, the refrigerant that is cooled by outside air of a very low temperature or a low temperature in winter is cooled by an interior condenser to be exhausted in a very low temperature condition to an outside condenser, and therefore ice is formed on a surface of the outside condenser and heat exchange efficiency of the heat exchange media and heating performance and efficiency are deteriorated, in a case that the cooling mode is transformed to the heating mode, the condensate that stays on the evaporator increases humidity such that moisture is formed on the interior of the glass of the vehicle.
To solve such problems, the compressor stops operating and warming is performed only by the PTC heater in a defrosting mode where a surface of the exterior condenser is defrosted. Therefore, heating performance may be seriously deteriorated, the heating load may be increased due to the increase of power consumption, and the mileage may be decreased when driving while warming.
In addition, since heat for converting the liquid refrigerant into a gaseous refrigerant is insufficient when the liquid refrigerant flows into the interior condenser, compressing efficiency may be deteriorated, heating performance may be seriously deteriorated when the air temperature is low, the system may be unstable, and durability of the compressor may be deteriorated when the liquid refrigerant flows into the compressor.
In addition, noise and vibration may occur due to a frequent open/close operation of a 2-way valve in a dehumidification mode where moisture is removed from the cabin of the vehicle.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.